DNA-topoisomerases are enzymes which are present in the nuclei of cells where they catalyze the breaking and rejoining of DNA strands, which control the topological state of DNA. Recent studies also suggest that topoisomerases are also involved in regulating template supercoiling during RNA transcription. There are two major classes of mammalian topoisomerases. DNA-topoisomerase-1 catalyzes changes in the topological state of duplex DNA by performing transient single-strand breakage-union cycles. In contrast, mammalian topoisomerase II alters the topology of DNA by causing a transient enzyme bridged double-strand break, followed by strand passing and resealing. Mammalian topoisomerase II has been further classified as Type II xcex1 and Type II xcex2. The antitumor activity associated with agents which are topoisomerase poisons is associated with their ability to stabilize the enzyme-DNA cleavable complex. This drug-induced stabilization of the enzyme-DNA cleavable complex effectively converts the enzyme into a cellular poison.
Several antitumor agents in clinical use have potent activity as mammalian topoisomerase II poisons. These include adriamycin, actinomycin D, daunomycin, VP-16, and VM-26 (teniposide or epipodophyllotoxin). In contrast to the number of clinical and experimental drugs which act as topoisomerase II poisons, there are currently only a limited number of agents which have been identified as topoisomerase I poisons. Camptothecin and its structurally-related analogs are among the most extensively studied topoisomerase I poisons. Recently, bi- and terbenzimidazoles (Chen et al., Cancer Res. 1993, 53, 1332-1335; Sun et al., J. Med. Chem. 1995, 38, 3638-3644; Kim et al., J. Med. Chem. 1996, 39, 992-998), certain benzo[c]phenanthridine and protoberberine alkaloids and their synthetic analogs (Makhey et al., Med. Chem. Res. 1995, 5, 1-12; Janin et al., J. Med. Chem 1975, 18, 708-713; Makhey et al., Bioorg. and Med. Chem. 1996, 4, 781-791), as well as the fungal metabolites, bulgarein (Fujii et al., J. Biol. Chem. 1993, 268, 13160-13165) and saintopin (Yamashita et al., Biochemistry 1991, 30, 5838-5845) and indolocarbazoles (Yamashita et al., Biochemistry 1992, 31, 12069-12075) have been identified as topoisomerase I poisons.
The exceptional topoisomerase poisoning observed with coralyne, nitidine, 5,6-dihydro-8-desmethylcoralyne and related analogs prompted several recent studies on those structural features which are associated with their ability to act specifically as poisons of topoisomerase I or topoisomerase II (Gatto et al., Cancer Res. 1996, 56, 2795-2800; Wang et al., Chem. Res. Toxicol. 1996, 9, 75-83; Wang et al., Chem. Res. Toxicol., 1993, 6, 813-818). A common feature associated with all three of these agents is the presence of a 3-phenylisoquinolinium moiety within their structure.
Despite the observation that several of these compounds had similar potency to camptothecin as a topoisomerase I poison or similar potency to VM-26 as a topoisomerase II poison, they possessed only modest cytotoxic activity. The absence of a more direct correlation with their potency as topoisomerase poisons was attributed, in part, to the likelihood that these agents are not likely to be absorbed as effectively into cells as either camptothecin or VM-26. The presence of the quaternary ammonium group most likely impedes cellular uptake. It has been speculated that agents such as coralyne and nitidine may need to undergo hydrolysis to permit effective transport, with subsequent dehydration or cyclodehydration to reform the quaternary ammonium parent compound. This may explain the relatively poor antitumor activity observed in vivo with agents such as coralyne or nitidine.
Presently, a need exists for novel anti-cancer agents, for anti-cancer agents that exhibit improved activity, and for anti-cancer agents that exhibit fewer side-effects or improved selectivity compared to existing agents.
The present invention provides compounds that show inhibitory activity against topoisomerase I and/or topoisomerase II, and compounds that are effective cytotoxic agents against cancer cells, including drug-resistant cancer cells. Accordingly, the invention provides a compound of the invention which is a compound of formula I: 
wherein
R1, R2, and R3 are each individually hydrogen, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C1-C6)alkoxy, nitro, hydroxy, NRgRh, COORk, ORm, or halo; or R1 and R2 taken together are methylenedioxy and R3 is hydrogen, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C1-C6)alkoxy, nitro, hydroxy, NRgRh, COORk, ORm, or halo; or R2 and R3 taken together are methylenedioxy and R1 is hydrogen, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C1-C6)alkoxy, nitro, hydroxy, NRgRh, COORk, ORm, or halo;
R4 is oxy, (C1-C6)alkyl, or is absent;
R5 is hydrogen, hydroxy, or (C1-C6)alkyl;
R6, R7 and R8 are each individually hydrogen, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C1-C6)alkoxy, nitro, hydroxy, NRgRh, COORk, ORm, or halo; or R6 and R7 taken together are methylenedioxy and R8 is hydrogen, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C1-C6)alkoxy, nitro, hydroxy, NRgRh, COORk, ORm, or halo; or R7 and R8 taken together are methylenedioxy and R6 is hydrogen, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C1-C6)alkoxy, nitro, hydroxy, NRgRh, C(xe2x95x90O)Rk, COORk, ORm, or halo;
each bond represented by xe2x80x94xe2x80x94xe2x80x94xe2x80x94xe2x80x94 is individually present or absent;
X is C(Ra)(Rb) or NRc;
Y is C(Rd)(Re) or NRf;
if present, Ra and Rb are each independently hydrogen or (C1-C6)alkyl if the bond between the 11- and 12-positions represented by xe2x80x94xe2x80x94xe2x80x94xe2x80x94xe2x80x94 is absent; or Ra is hydrogen or (C1-C6)alkyl and Rb is absent if the bond between the 11- and 12-positions represented by xe2x80x94xe2x80x94xe2x80x94xe2x80x94xe2x80x94 is present;
if present, Rc and Rf are each independently hydrogen or (C1-C6)alkyl if the bond between the 11- and 12-positions represented by xe2x80x94xe2x80x94xe2x80x94xe2x80x94xe2x80x94 is absent; or Rc and Rf are each independently (C1-C6)alkyl or absent if the bond between the 11- and 12-positions represented by xe2x80x94xe2x80x94xe2x80x94xe2x80x94xe2x80x94 is present;
if present, Rd and Re are each independently hydrogen or (C1-C6)alkyl if the bond between the 11- and 12-positions represented by xe2x80x94xe2x80x94xe2x80x94xe2x80x94xe2x80x94 is absent; or Rd is hydrogen or (C1-C6)alkyl and Re is absent if the bond between the 11- and 12-positions represented by xe2x80x94xe2x80x94xe2x80x94xe2x80x94xe2x80x94 is present;
each Rg and Rh is independently hydrogen, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C1-C6)alkoxy, (C1-C6)alkanoyl, aryl, aryl(C1-C6)alkyl, aryloxy, or aryl(C1-C6)alkoxy; or Rg and Rh together with the nitrogen to which they are attached are pyrrolidino, piperidino, morpholino, or thiomorpholino;
each Rk is independently hydrogen, or (C1-C6)alkyl; and
each Rm is independently (C1-C6)alkanoyl, aryl, or aryl(C1-C6)alkyl;
wherein any (C1-C6)alkyl, (C3-C6)cycloalkyl, or (C1-C6)alkoxy of R1, R2, R3, R6, R7, R8, or Rk is optionally substituted on carbon with 1, 2, or 3 substituents independently selected from hydroxy, halo, NRnRp, (C3-C6)cycloalkyl, or (C1-C6)alkoxy; wherein each Rn and Rp is independently hydrogen, (C1-C6)alkyl, (C3-C6)cycloalkyl, (C1-C6)alkoxy, or (C1-C6)alkanoyl; or Rn and Rp together with the nitrogen to which they are attached are pyrrolidino, piperidino, morpholino, or thiomorpholino;
wherein any aryl is optionally be substituted with 1, 2, or 3 substituents independently selected from hydroxy, halo, nitro, trifluoromethyl, trifluoromethoxy, carboxy, amino, (C1-C6)alkyl, (C3-C6)cycloalkyl, and (C1-C6)alkoxy;
provided that at least one of R2 and R8 is hydrogen, methyl, nitro, hydroxy, amino, fluoro or chloro; or at least one of R2 and R8 forms part of a methylenedioxy; and
provided that R1-R3 and R6-R8 are not all hydrogen;
or a pharmaceutically acceptable salt thereof.
The invention also provides a pharmaceutical composition comprising a effective amount of a compound of formula I, or a pharmaceutically acceptable salt thereof, in combination with a pharmaceutically acceptable diluent or carrier.
The invention also provides a method of inhibiting cancer cell growth, comprising administering to a mammal afflicted with cancer, an amount of a compound of formula (I), effective to inhibit the growth of said cancer cells.
The invention also provides a method comprising inhibiting cancer cell growth by contacting said cancer cell in vitro or in vivo with an amount of a compound of claim 1, effective to inhibit the growth of said cancer cell.
The invention also provides a compound of formula I for use in medical therapy (preferably for use in treating cancer, e.g. solid tumors), as well as the use of a compound of formula I for the manufacture of a medicament useful for the treatment of cancer, e.g. solid tumors.
The invention also provides processes and novel intermediates disclosed herein which are useful for preparing compounds of the invention. Some of the compounds of formula I are useful to prepare other compounds of formula I.